1. Field of the Invention
The present invention relates to a non-contact type information card for data communication with an external unit and a communication system using the same.
2. Description of the Related Art
Of various types of information cards, information cards of a non-contact type have been utilized in recent years which employ a space transmitting medium, such as electromagnetic waves or light, to transmit and receive signals. FIG. 14 shows the structure of such a non-contact type information card. A ROM 2 and a RAM 3 are connected through a bus 8 to a CPU 1 controlling the operation of the information card. An input/output control circuit 4 (hereinafter referred to as an I/O control circuit 4) for controlling the input and output of data is connected to the bus 8. An antenna 6 is connected to the I/O control circuit 4 via a modulating/demodulating circuit 5. The information card has a built-in battery 7 which supplies electricity to electric circuits.
In such an information card, when the antenna 6 receives a command signal in the form of an electromagnetic wave from an external unit, such as terminal equipment, the command signal is input to the CPU 1 through the I/O control circuit 4 after having been demodulated by the modulating/demodulating circuit 5. The CPU 1 deciphers the command signal, and then creates a predetermined response signal. The response signal is input via the I/O control circuit 4 to the modulating/demodulating circuit 5, which modulates it before the response signal is transmitted to the external unit through the antenna 6.
Such an information card is used to control the ingress/egress of a special area 91, such as a partitioned room or a hall, as shown in FIG. 15. In the special area 91, there is an entrance gate 92 provided with entrance terminal equipment 94 and an exit gate 93 provided with exit terminal equipment 95. The entrance terminal equipment 94 constantly sends out at predetermined time intervals the command signal that includes a place code indicating the entrance gate 92 and a time code indicating when an information card holder passes the entrance gate 92. Similarly, the exit terminal equipment 95 constantly sends out at the predetermined time intervals the command signal that includes a place code indicating the exit gate 93 and a time code indicating when a card holder passes the exit gate 93. For this reason, every time card holders pass the entrance gate 92 or the exit gate 93, the place code and the time code are recorded onto the information card. By collecting the information cards, onto which the time and place codes are recorded, it is thus possible to control the ingress/egress of the special area 91, and to determine the number of entrances/exits made.
However, the entrance terminal equipment 94 installed at the entrance gate 92 and the exit terminal equipment 95 at the exit gate 93 regularly send out the command signal at the predetermined time intervals. Therefore, when an area around the gates becomes crowded and an information card holder stops in the zone where the command signal can be transmitted, the information card regularly continues to receive the command signal from the terminal equipment 94 or 95. Thus, every time the information card receives the command signal, it transmits the response signal. In this way, if the information card performs its operation a plurality of times with respect to only one passage through either gate, it becomes impossible to accurately control ingress/egress, and impossible to determine the number of entrances/exits made. In other words, it is required that the information card be limited to only one operation for each passage through either gate.
Several methods can be employed for limiting to only one operation for each passage, such as by moving the information card immediately outside the zone where the command signal can be transmitted; making the time intervals at which the terminal equipment transmits the command signal longer; and providing a period during which the information card restricts the reception of the command signal after it has transmitted the response signal.
These methods, however, limit the methods of carrying the information card, or cause a decrease in the processing speed when a large number of information cards are processed successively.